Light Modulation Device

ABSTRACT

A light modulation device is disclosed herein. In some embodiments, a light modulation device includes a first polymer film substrate, a second polymer film substrate, an active liquid crystal layer disposed between the first and second polymer film substrates, a reflective layer, wherein the active liquid crystal layer is capable of switching between a first orientation state and a second orientation state different from the first orientation state upon application of a voltage, each of the polymer film substrates has an in-plane retardation of 4,000 nm or more for light having a wavelength of 550 nm, a ratio of an elongation (E1) in a first direction to an elongation (E2) in a second direction perpendicular to the first direction of 3 or more, and wherein an angle formed by the first directions of the first and second polymer film substrates is in a range of 0 degrees to 10 degrees.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a national phase entry under 35 U.S.C. § 371of International Application No. PCT/KR2018/005016, filed on Apr. 30,2018, which claims priority from Korean Patent Application No.10-2017-0054964, filed on Apr. 28, 2017, Korean Patent Application No.10-2018-0003783, Korean Patent Application No. 10-2018-0003784, KoreanPatent Application No. 10-2018-0003785, Korean Patent Application No.10-2018-0003786, Korean Patent Application No. 10-2018-0003787, KoreanPatent Application No. 10-2018-0003788, Korean Patent Application No.10-2018-0003789, filed on Jan. 11, 2018, and Korean Patent ApplicationNo. 10-2018-0004305, filed on Jan. 12, 2018, the disclosures of whichare incorporated by reference herein.

TECHNICAL FIELD

This application relates to a light modulation device.

BACKGROUND ART

A light modulation device, in which a light modulation layer including aliquid crystal compound or the like is positioned between two substratesfacing each other, has been used for various applications.

For example, in Patent Document 1 (EP Patent Application Publication No.0022311) a variable transmittance device using a so-called GH cell(guest host cell), in which a mixture of a liquid crystal host materialand a dichroic dye guest is applied, as a light modulation layer hasbeen known.

In such a device, a glass substrate having excellent optical isotropyand good dimensional stability has mainly been used as the substrate.

There is an attempt to apply a polymer film substrate instead of a glasssubstrate as a substrate of the light modulation device, while theapplication of the light modulation device is extended to eyewear or asmart window such as a sunroof without being limited to the displaydevice and the shape of the device is not limited to a plane, butvarious designs such as a folding form are applied thereto, with showingthe necessity of a so-called flexible device or the like.

In the case of applying the polymer film substrate, it is known that itis advantageous to apply a film substrate which is as opticallyisotropic as possible and has a small difference in physical propertiesin so-called MD (machine direction) and TD (transverse direction)directions in order to secure characteristics similar to those of aglass substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an exemplary light modulation device ofthe present application.

FIG. 2 illustratively shows eyewear.

FIGS. 3 and 4 show durability evaluation results for Examples andComparative Examples.

DISCLOSURE Technical Problem

The present application relates to a light modulation device. It is anobject of the present application to provide a light modulation devicewhich is excellent in both mechanical properties and optical propertiesby applying an optically and mechanically anisotropic polymer film as asubstrate.

Technical Solution

In this specification, the term such as vertical, horizontal, orthogonalor parallel among terms defining an angle means substantially vertical,horizontal, orthogonal or parallel in the range without impairingintended effects, and the range of vertical, horizontal, orthogonal orparallel includes an error such as a production error or a deviation(variation). For example, each case of the foregoing may include anerror within about ±15 degrees, an error within about ±10 degrees or anerror within about ±5 degrees.

Among physical properties mentioned herein, when the measuredtemperature affects relevant physical properties, the physicalproperties are physical properties measured at room temperature, unlessotherwise specified.

In this specification, the term room temperature is a temperature in astate without particularly warming or cooling, which may mean onetemperature in a range of about 10° C. to 30° C., for example, atemperature of about 15° C. or higher, 18° C. or higher, 20° C. orhigher, or about 23° C. or higher, and about 27° C. or lower. Unlessotherwise specified, the unit of the temperature mentioned herein is °C.

The phase difference and the refractive index mentioned herein mean arefractive index for light having a wavelength of about 550 nm, unlessotherwise specified.

Unless otherwise specified, the angle formed by any two directions,which is mentioned herein, may be an acute angle of acute angles toobtuse angles formed by the two directions, or may be a small angle fromangles measured in clockwise and counterclockwise directions. Thus,unless otherwise specified, the angles mentioned herein are positive.However, in order to display the measurement direction between theangles measured in the clockwise direction or the counterclockwisedirection if necessary, any one of the angle measured in the clockwisedirection and the angle measured in the counterclockwise direction maybe represented as a positive number, and the other angle may berepresented as a negative number.

The liquid crystal compound included in the active liquid crystal layeror the light modulation layer herein may also be referred to as liquidcrystal molecules, a liquid crystal host (when included with thedichroic dye guest), or simply liquid crystals.

The present application relates to a light modulation device. The termlight modulation device may mean a device capable of switching betweenat least two or more different light states. Here, the different lightstates may mean states in which at least the transmittance and/or thereflectance are different.

An example of the state that the light modulation device can implementincludes a transmission mode state, a blocking mode state, a highreflection mode state and/or a low reflection mode state.

In one example, the light modulation device, at least, may be a devicecapable of switching between the transmission mode state and theblocking mode state, or may be a device capable of switching between thehigh reflection mode and the low reflection mode.

The transmittance of the light modulation device in the transmissionmode may be at least 20% or more, 25% or more, 30% or more, 35% or more,40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% ormore, 70% or more, 75% or more, or 80% or more or so. Also, thetransmittance of the light modulation device in the blocking mode may be60% or less, 55% or less, 50% or less, 45% or less, 40% or less, 35% orless, 30% or less, 25% or less, 20% or less, 15% or less, 10% or less,or 5% or less. Since the higher the transmittance in the transmissionmode state is, the more advantageous it is and the lower thetransmittance in the blocking mode state is, the more advantageous itis, the upper limit of the transmittance in the transmission mode stateand the lower limit of the transmittance in the blocking mode state arenot particularly limited, where in one example, the upper limit of thetransmittance in the transmission mode state may be about 100% and thelower limit of the transmittance in the blocking mode state may be about0%.

In one example, in the light modulation device capable of switchingbetween the transmission mode state and the blocking mode state, thedifference between the transmittance in the transmission mode state andthe transmittance in the blocking mode state (transmission mode -blocking mode) may be 15% or more, 20% or more, 25% or more, 30% ormore, 35% or more, or 40% or more, or may be 90% or less, 85% or less,80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% orless, 50% or less, or 45% or less.

The above-mentioned transmittance may be, for example, linear lighttransmittance. The linear light transmittance is a percentage of theratio of the light transmitted in the same direction as the incidentdirection to the light incident on the device. For example, if thedevice is in the form of a film or sheet, the percentage of the lighttransmitted through the device in the direction parallel to the normaldirection among the light incident in a direction parallel to the normaldirection of the film or sheet surface may be defined as thetransmittance.

The reflectance of the light modulation device in the high reflectionmode state may be at least 10% or more, 15% or more, 20% or more, 25% ormore, 30% or more, 35% or more, or 40% or more. Also, the reflectance ofthe light modulation device in the low reflection mode state may be 20%or less, 15% or less, 10% or less, 7% or less, 6% or less, 5% or less,or 4% or less. Since the higher the reflectance in the high reflectancemode is, the more advantageous it is and the lower the reflectance inthe low reflectance mode is, the more advantageous it is, the upperlimit of the reflectance in the high reflection mode state and the lowerlimit of the reflectance in the low reflection mode state are notparticularly limited, where in one example, the reflectance in the highreflection mode state may be about 100% or less, about 90% or less,about 80% or less, about 70% or less, about 60% or less, 55% or less,50% or less, or about 40% or less or so, and the reflectance in the lowreflection mode state may be about 0% or more, about 0.1% or more, 1% ormore, 3% or more, or 5% or more.

Besides, in one example, in the light modulation device capable ofswitching between the low reflection mode state and the high reflectionmode state, the difference between the reflectance in the highreflection mode state and the reflectance in the low reflection modestate (high reflection mode - low reflection mode) may be 5% or more,10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% ormore, or 40% or more, or may be 90% or less, 85% or less, 80% or less,75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% orless, or 45% or less.

The above-mentioned transmittance and reflectance may be eachtransmittance or reflectance for any one wavelength in the visible lightregion, for example, any one wavelength in a range of about 400 to 700nm or about 380 to 780 nm, or transmittance or reflectance for theentire visible light region, maximum or minimum transmittance orreflectance among the transmittance or reflectance for the entirevisible light region, or an average value of the transmittance or anaverage value of the reflectance in the visible region.

The light modulation device of the present application may be designedto switch between at least two or more states of any one state selectedfrom the transmission mode, the blocking mode, the high reflection modeand the low reflection mode, and another state. If necessary, otherstates other than the above states, for example, other third states orfurther states including an intermediate transmittance state in thetransmission mode and blocking mode states, an intermediate reflectancestate in the high reflection mode and low reflection mode states, or thelike can also be implemented.

The switching of the light modulation device may be controlled dependingon whether or not an external signal, for example, a voltage signal isapplied. For example, in a state of not applying an external signal suchas a voltage, the light modulation device may maintain any one of theabove-described states, and then may be switched to another state when avoltage is applied. The state of the mode may be changed or the thirddifferent mode state may also be implemented, by changing the intensity,frequency and/or shape of the applied voltage.

The light modulation device of the present application may basicallycomprise a light modulation film layer having two substrates disposedopposite to each other and a light modulation layer positioned betweenthe substrates. Hereinafter, for convenience, any one of the twosubstrates disposed opposite to each other will be referred to as afirst substrate, and the other substrate will be referred to as a secondsubstrate.

FIG. 1 is a cross-sectional diagram of an exemplary light modulationfilm layer (active liquid crystal film layer) of the presentapplication, where the light modulation film layer may comprise firstand second polymer film substrates (11, 13), and a light modulationlayer (12) present between the first and second polymer film substrates.

In the light modulation device of the present application, a polymerfilm substrate is applied as the substrate. The substrate of the lightmodulation device may not comprise a glass layer. The presentapplication can constitute a device having no optical defect such as aso-called rainbow phenomenon but excellent mechanical properties, bydisposing polymer film substrates having optically large anisotropy andalso anisotropy even in terms of mechanical properties in a specificrelationship. Such a result is contrary to the common sense of the priorart that optically isotropic substrates must be applied in order tosecure excellent optical properties and substrates having isotropicmechanical properties are advantageous in terms of mechanical propertiessuch as dimensional stability of the device.

In this specification, the polymer film substrate having anisotropy interms of optical and mechanical properties may be referred to as anasymmetric substrate or an asymmetric polymer film substrate. Here, thefact that the polymer film substrate is optically anisotropic is thecase of having the above-described in-plane retardation, and the factthat it is anisotropic in terms of mechanical properties is the case ofhaving physical properties to be described below.

Hereinafter, physical properties of the polymer film substrate mentionedherein may be physical properties of the polymer film substrate itself,or physical properties in a state where an electrode layer is formed onone side of the polymer film substrate. In this case, the electrodelayer may be an electrode layer formed in a state where the polymer filmsubstrate is included in the optical device.

Measurement of physical properties of each polymer film substratementioned herein is performed according to the method described in theexample section of this specification.

In one example, the in-plane retardation of the first and second polymerfilm substrates may be about 4,000 nm or more, respectively.

In this specification, the in-plane retardation (Rin) may mean a valuecalculated by Equation 1 below.

Rin=d×(nx−ny)   [Equation 1]

In Equation 1, Rin is in-plane retardation, d is a thickness of thepolymer film substrate, nx is a refractive index in the in-plane slowaxis direction of the polymer film substrate, ny is a refractive indexin the fast axis direction, which is the refractive index of thein-plane direction perpendicular to the slow axis direction.

The in-plane retardation of each of the first and second polymer filmsubstrates may be 4,000 nm or more, 5,000 nm or more, 6,000 nm or more,7,000 nm or more, 8,000 nm or more, 9,000 nm or more, 10,000 nm or more,11,000 nm or more, 12,000 nm or more, 13,000 nm or more, 14,000 nm ormore, or 15,000 nm or more or so. The in-plane retardation of each ofthe first and second polymer film substrates may be about 50,000 nm orless, about 40,000 nm or less, about 30,000 nm or less, 20,000 nm orless, 18,000 nm or less, 16,000 nm or less, 15,000 nm or less, or 12,000nm or less or so.

As a polymer film having large retardation as above, a film known as aso-called high-stretched PET (poly(ethylene terephthalate)) film or SRF(super retardation film), and the like is typically known. Therefore, inthe present application, the polymer film substrate may be, for example,a polyester film substrate.

The film having extremely high retardation as above is known in the art,and such a film exhibits high asymmetry even in mechanical properties byhigh stretching or the like during preparation procedures as well asoptically large anisotropy. A representative example of the polymer filmsubstrate in a state known in the art is a polyester film such as a PET(poly(ethylene terephthalate)) film, and for example, there are films ofthe trade name SRF (super retardation film) series supplied by ToyoboCo., Ltd.

Unless otherwise specified, each of the polymer film substrates may havea thickness direction retardation value of about 1,000 nm or less ascalculated by Equation 2 below.

Rth=d×(nz−ny)   [Equation 2]

In Equation 2, Rth is thickness direction retardation, d is a thicknessof the polymer film substrate, and ny and nz are refractive indexes inthe y axis and z axis directions of the polymer film substrate,respectively. The y axis of the polymer film substrate is the in-planefast axis direction, and the z axis direction means the thicknessdirection of the polymer film substrate.

The polymer film substrate may also have gas permeability of less than0.002 GPU at room temperature. The gas permeability of the polymer filmsubstrate may be, for example, 0.001 GPU or less, 0.0008 GPU or less,0.006 GPU or less, 0.004 GPU or less, 0.002 GPU or less, or 0.001 GPU orless. When the gas permeability of the polymer film substrate is withinthe above range, it is possible to provide a light modulation devicehaving excellent durability in which void generation by an external gasis suppressed. The lower limit of the range of the gas permeability isnot particularly limited. That is, the gas permeability is moreadvantageous, as the value is smaller.

In one example, in each of the polymer film substrates, a ratio (E1/E2)of an elongation (El) in any first direction in the plane to anelongation (E2) in a second direction perpendicular to the firstdirection may be 3 or more. In another example, the ratio (E1/E2) may beabout 3.5 or more, 4 or more, 4.5 or more, 5 or more, 5.5 or more, 6 ormore, or 6.5 or more. In another example, the ratio (E1/E2) may be about20 or less, 18 or less, 16 or less, 14 or less, 12 or less, 10 or less,8 or less, or 7.5 or less.

As used herein, the terms “first direction,” “second direction” and“third direction” of the polymer film substrate are each any in-planedirection of the film substrate. For example, when the polymer filmsubstrate is a stretched polymer film substrate, the in-plane directionmay be an in-plane direction formed by MD (machine direction) and TD(transverse direction) directions of the polymer film substrate. In oneexample, the first direction described herein may be any one of the slowaxis direction and the fast axis direction of the polymer filmsubstrate, and the second direction may be the other of the slow axisdirection and the fast axis direction. In another example, when thepolymer film substrate is a stretched polymer film substrate, the firstdirection may be any one of MD (machine direction) and TD (transversedirection) directions, and the second direction may be the other of MD(machine direction) and TD (transverse direction) directions.

In one example, the first direction of the polymer film substratementioned herein may be the TD direction or the slow axis direction.

Here, each of the first and second polymer film substrates may have theelongation in the first direction (for example, the above-described slowaxis direction or TD direction) of 15% or more, or 20% or more. Inanother example, the elongation may be about 25% or more, 30% or more,35% or more, or 40% or more, or may be about 100% or less, 90% or less,80% or less, 70% or less, about 60% or less, 55% or less, 50% or less,or 45% or less.

In one example, in each of the first and second polymer film substrates,an elongation (E3) in a third direction forming an angle within a rangeof 40 degrees to 50 degrees or about 45 degrees with the first andsecond directions, respectively, is larger than the elongation (E1) inthe first direction (for example, the above-described slow axialdirection or TD direction), where the ratio (E3/E2) of the elongation(E3) in the third direction to the elongation (E2) in the seconddirection may be 5 or more.

In another example, the ratio (E3/E2) may be 5.5 or more, 6 or more, 6.5or more, 7 or more, 7.5 or more, 8 or more, or 8.5 or more, and may beabout 20 or less, 18 or less, 16 or less, 14 or less, 12 or less, or 10or less.

Here, each of the first and second polymer film substrates may have theelongation in the third direction of 30% or more. In another example,the elongation may be about 35% or more, 40% or more, 45% or more, 50%or more, or 55% or more, or may be about 80% or less, 75% or less, 70%or less, or 65% or less.

In each of the first and second polymer film substrates, a ratio(CTE2/CTE1) of a coefficient of thermal expansion (CTE2) in the seconddirection to a coefficient of thermal expansion (CTE1) in the firstdirection (for example, the above-described slow axis direction or TDdirection) may be 1.5 or more. The coefficients of thermal expansion(CTE1, CTE2) are each a value confirmed within a temperature range of40° C. to 80° C. In another example, the ratio (CTE2/CTE1) may be about2 or more, about 2.5 or more, 3 or more, or 3.5 or more, or may be 10 orless, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, or 4 orless.

The coefficient of thermal expansion (CTE2) in the second direction maybe in a range of 5 to 150 ppm/° C. The coefficient of thermal expansionmay be about 10 ppm/° C. or more, 15 ppm/° C. or more, 20 ppm/° C. ormore, 25 ppm/° C. or more, 30 ppm/° C. or more, 35 ppm/° C. or more, 40ppm/° C. or more, 45 ppm/° C. or more, 50 ppm/° C. or more, 55 ppm/° C.or more, 60 ppm/° C. or more, 65 ppm/° C. or more, 70 ppm/° C. or more,75 ppm/° C. or more, or 80 ppm/° C. or more, or may be 140 ppm/° C. orless, 130 ppm/° C. or less, 120 ppm/° C. or less, 100 ppm/° C. or less,95 ppm/° C. or less, 90 ppm/° C. or less, 85 ppm/° C. or less, 80 ppm/°C. or less, 40 ppm/° C. or less, 30 ppm/° C. or less, or 25 ppm/° C. orless.

In each of the first and second polymer film substrates, a ratio(YM1/YM2) of an elastic modulus (YM1) in the first direction (forexample, the above-described slow axis direction or TD direction) to anelastic modulus (YM2) in the second direction may be 1.5 or more. Inanother example, the ratio (YM1/YM2) may be about 2 or more, or may be10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 orless, 3 or less or 2.5 or less.

The elastic modulus (YM1) in the first direction (for example, theabove-described slow axis direction or TD direction) may be in a rangeof about 2 to 10 GPa. In another example, the elastic modulus (YM1) maybe about 2.5 GPa or more, 3GPa or more, 3.5 GPa or more, 4 GPa or more,4.5 GPa or more, 5 GPa or more, or 5.5 GPa or more, or may also be about9.5 GPa or less, 9 GPa or less, 8.5 GPa or less, 8 GPa or less, 7.5 GPaor less, 7 GPa or less, 6.5 GPa or less, or 6 GPa or less.

The elastic modulus is a so-called Young's modulus, which is measuredaccording to the method of the example described below.

In each of the first and second polymer film substrates, a ratio(MS1/MS2) of a maximum stress (MS1) in the first direction (for example,the above-described slow axis direction or TD direction) to a maximumstress (MS2) in the second direction may be 1.5 or more. In anotherexample, the ratio (MS1/MS2) may be about 2 or more, or may be 10 orless, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less,3 or less, or 2.5 or less.

The maximum stress (MS1) in the first direction (for example, theabove-described slow axis direction or TD direction) may be in a rangeof about 80 to 300 MPa. In another example, the maximum stress (MS1) maybe about 90 MPa or more, about 100 MPa or more, about 110 MPa or more,about 120 MPa or more, about 130 MPa or more, about 140 MPa or more,about 150 MPa or more, about 155 MPa or more, 160 MPa or more, 165 MPaor more, 170 MPa or more, 175 MPa or more, or 180 MPa or more, or mayalso be about 300 MPa or less, about 290 MPa or less, about 280 MPa orless, about 270 MPa or less, about 260 MPa or less, about 250 MPa orless, about 245 MPa or less, 240 MPa or less, 235 MPa or less, 230 MPaor less, 225 MPa or less, 220 MPa or less, 215 MPa or less, 210 MPa orless, 205 MPa or less, 200 MPa or less, 195 MPa or less, or 190 MPa orless.

In the light modulation device of the present application, an absolutevalue of the angle formed by the first direction of the first polymerfilm substrate and the first direction of the second polymer filmsubstrate may be in a range of 0 degrees to 10 degrees or 0 degrees to 5degrees, or the first directions may be approximately horizontal to eachother. The first direction may be the slow axis direction or the TDdirection of the polymer film substrate as described above.

As the device is configured by disposing polymer film substrates havingasymmetric optical and mechanical properties so as to have such aspecific relationship as described above, the present application canrealize excellent optical and mechanical properties.

Although the reason why such an effect is realized is not clear, it isassumed that it is because a better balance of optical and mechanicalproperties is secured by controlling the large asymmetry, in which atleast two polymer film substrates have, similarly and again disposingboth asymmetry to be symmetric based on a specific axis, as comparedwith application of a film having an isotropic structure.

The thickness of each of the first and second polymer film substrates isnot particularly limited, which may be set in an appropriate rangedepending on the purpose. Typically, the thickness may be in a range ofabout 10 μm to 200 μm.

As described above, a representative example of the polymer film havinglarge optical and mechanical asymmetry as above is a stretched PET(polyethyleneterephtalate) film known as a so-called high stretchedpolyester film or the like, and such a film is easily available in theindustry.

Usually, the stretched PET film is a uniaxially stretched film of one ormore layers produced by forming a PET-based resin into a film withmelting/extruding, and stretching it or a biaxially stretched film ofone or more layers produced by longitudinally and transverselystretching it after film formation.

The PET-based resin generally means a resin in which 80 mol% or more ofthe repeating units are ethylene terephthalate, which may also containother dicarboxylic acid components and diol components. Otherdicarboxylic acid components are not particularly limited, but mayinclude, for example, isophthalic acid, p-beta-oxyethoxybenzoic acid,4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone,bis(4-carboxyphenyl)ethane, adipic acid, sebacic acid and/or1,4-dicarboxycyclohexane, and the like.

Other diol components are not particularly limited, but may includepropylene glycol, butanediol, neopentyl glycol, diethylene glycol,cyclohexanediol, ethylene oxide adducts of bisphenol A, polyethyleneglycol, polypropylene glycol and/or polytetramethylene glycol, and thelike.

The dicarboxylic acid component or the diol component may be used incombination of two or more as necessary. Furthermore, an oxycarboxylicacid such as p-oxybenzoic acid may also be used in combination. Inaddition, as other copolymerization components, a dicarboxylic acidcomponent containing a small amount of amide bonds, urethane bonds,ether bonds and carbonate bonds, and the like, or a diol component mayalso be used.

As a production method of the PET-based resin, a method of directlypolycondensing terephthalic acid, ethylene glycol and/or, as necessary,other dicarboxylic acids or other diols, a method of transesterifyingdialkyl ester of terephthalic acid and ethylene glycol and/or, asnecessary, dialkyl esters of other dicarboxylic acids or other diols andthen polycondensing them, and a method of polycondensing terephtalicacid and/or, as necessary, ethylene glycol esters of other dicarboxylicacids and/or, as necessary, other diolesters, and the like are adopted.

For each polymerization reaction, a polymerization catalyst containingan antimony-based, titanium-based, germanium-based or aluminum-basedcompound, or a polymerization catalyst containing the composite compoundcan be used.

The polymerization reaction conditions can be appropriately selecteddepending on monomers, catalysts, reaction apparatuses and intendedresin physical properties, and are not particularly limited, but forexample, the reaction temperature is usually about 150° C. to about 300°C., about 200° C. to about 300° C. or about 260° C. to about 300° C.Furthermore, the reaction pressure is usually atmospheric pressure toabout 2.7 Pa, where the pressure may be reduced in the latter half ofthe reaction.

The polymerization reaction proceeds by volatilizing leaving reactantssuch as a diol, an alkyl compound or water.

The polymerization apparatus may also be one which is completed by onereaction tank or connects a plurality of reaction tanks. In this case,the reactants are polymerized while being transferred between thereaction tanks, depending on the degree of polymerization. In addition,a method, in which a horizontal reaction apparatus is provided in thelatter half of the polymerization and the reactants are volatilizedwhile heating/kneading, may also be adopted.

After completion of the polymerization, the resin is discharged from thereaction tank or the horizontal reaction apparatus in a molten state,and then, obtained in the form of flakes cooled and pulverized in acooling drum or a cooling belt, or in the form of pellets tailored afterbeing introduced into an extruder and extruded in a string shape.Furthermore, solid-phase polymerization may be performed as needed,thereby improving the molecular weight or decreasing the low molecularweight component. As the low molecular weight component that may becontained in the PET resin, a cyclic trimer component may beexemplified, but the content of such a cyclic trimer component in theresin is usually controlled to 5,000 ppm or less, or 3,000 ppm or less.

The molecular weight of the PET-based resin is usually in a range of0.45 to 1.0 dL/g, 0.50 to 1.0 dL/g or 0.52 to 0.80 dL/g, when the resinhas been dissolved in a mixed solvent of phenol/tetrachloroethane =50/50(weight ratio) and it has been represented as a limiting viscositymeasured at 30° C.

In addition, the PET-based resin may contain additives as required. Theadditive may include a lubricant, an anti-blocking agent, a heatstabilizer, an antioxidant, an antistatic agent, a light stabilizer andan impact resistance improver, and the like. The addition amount thereofis preferably within a range that does not adversely affect the opticalproperties.

The PET-based resin is used in the form of pellets assembled by anordinary extruder, for formulation of such additives and film molding tobe described below. The size and shape of the pellets are notparticularly limited, but they are generally a cylindrical, spherical orflat spherical shape having both height and diameter of 5 mm or less.The PET-based resin thus obtained can be molded into a film form andsubjected to a stretching treatment to obtain a transparent andhomogeneous PET film having high mechanical strength. The productionmethod thereof is not particularly limited, and for example, thefollowing method is adopted.

Pellets made of the dried PET resin are supplied to a melt extrusionapparatus, heated to a melting point or higher and melted. Next, themelted resin is extruded from the die and quenched and solidified on arotary cooling drum to a temperature below the glass transitiontemperature to obtain an un-stretched film in a substantially amorphousstate. This melting temperature is determined according to the meltingpoint of the PET-based resin to be used or the extruder, which is notparticularly limited, but is usually 250° C. to 350° C. In order toimprove planarity of the film, it is also preferred to enhance adhesionbetween the film and the rotary cooling drum, and an adhesion method byelectrostatic application or an adhesion method by liquid coating ispreferably adopted. The adhesion method by electrostatic application isusually a method in which linear electrodes are provided on the uppersurface side of a film in a direction perpendicular to the flow of thefilm and a direct current voltage of about 5 to 10 kV is applied to theelectrodes to provide static charges to the film, thereby improving theadhesion between the rotary cooling drum and the film. In addition, theadhesion method by liquid coating is a method for improving the adhesionbetween the rotary cooling drum and the film by uniformly coating aliquid to all or a part (for example, only the portion in contact withboth film ends) of the surface of the rotary cooling drum. Both of themmay also be used in combination if necessary. The PET-based resin to beused may be mixed with two or more resins, or resins having differentstructures or compositions, if necessary. For example, it may includeusing a mixture of pellets blended with a particulate filling materialas an anti-blocking agent, an ultraviolet absorbing agent or anantistatic agent, and the like, and non-blended pellets, and the like.

Furthermore, the laminating number of films to be extruded may also betwo or more layers, if necessary. For example, it may include thatpellets blended with a particulate filling material as an anti-blockingagent and non-blended pellets are prepared and supplied from the otherextruder to the same die to extrude a film composed of two kinds andthree layers, “blended with filling material/no-blended/blended withfilling material,” and the like.

The un-stretched film is usually stretched longitudinally at atemperature not lower than the glass transition temperature in theextrusion direction first. The stretching temperature is usually 70 to150° C., 80 to 130° C., or 90 to 120° C. In addition, the stretchingratio is usually 1.1 to 6 times or 2 to 5.5 times. The stretching may beterminated once or divided into more than once as necessary.

The longitudinally stretched film thus obtained may be subjected to aheat treatment thereafter. Then, a relaxation treatment may be performedif necessary. The heat treatment temperature is usually 150 to 250° C.,180 to 245° C. or 200 to 230° C. Also, the heat treatment time isusually 1 to 600 seconds or 1 to 300 seconds or 1 to 60 seconds.

The temperature of the relaxation treatment is usually 90 to 200° C. or120 to 180° C. Also, the amount of relaxation is usually 0.1 to 20% or 2to 5%. The relaxation treatment temperature and the relaxation amountcan be set so that a heat shrinkage rate of the PET film afterrelaxation treatment at 150° C. is 2% or less.

In the case of obtaining uniaxially stretched and biaxially stretchedfilms, transverse stretching is usually performed by a tenter after thelongitudinal stretching treatment or after the heat treatment orrelaxation treatment, if necessary. The stretching temperature isusually 70 to 150° C., 80 to 130° C., or 90 to 120° C. In addition, thestretching ratio is usually 1.1 to 6 times or 2 to 5.5 times.Thereafter, the heat treatment and, if necessary, the relaxationtreatment can be performed. The heat treatment temperature is usually150 to 250° C. or 180 to 245° C. or 200 to 230° C. The heat treatmenttime is usually 1 to 600 seconds, 1 to 300 seconds, or 1 to 60 seconds.

The temperature of the relaxation treatment is usually 100 to 230° C.,110 to 210° C. or 120 to 180° C. Also, the relaxation amount is usually0.1 to 20%, 1 to 10%, or 2 to 5%. The relaxation treatment temperatureand the relaxation amount can be set so that the heat shrinkage rate ofthe PET film after the relaxation treatment at 150° C. is 2% or less.

In uniaxial stretching and biaxial stretching treatments, in order toalleviate deformation of the orientation main axis as represented bybowing, the heat treatment can be performed again or the stretchingtreatment can be performed after the transverse stretching. The maximumvalue of deformation in the orientation main axis by bowing with respectto the stretching direction is usually within 45 degrees, within 30degrees, or within 15 degrees. Here, the stretching direction alsorefers to a stretching large direction in longitudinal stretching ortransverse stretching.

In the biaxial stretching of the PET film, the transverse stretchingratio is usually slightly larger than the longitudinal stretching ratio,where the stretching direction refers to a direction perpendicular tothe long direction of the film. Also, the uniaxial stretching is usuallystretched in the transverse direction as described above, where thestretching direction equally refers to a direction perpendicular to thelong direction.

Also, the orientation main axis refers to a molecular orientationdirection at any point on the stretched PET film. Furthermore, thedeformation of the orientation main axis with respect to the stretchingdirection refers to an angle difference between the orientation mainaxis and the stretching direction. In addition, the maximum valuethereof refers to a maximum value of the values on the verticaldirection with respect to the long direction.

The direction of identifying the orientation main axis is known, and forexample, it can be measured using a retardation film/optical materialinspection apparatus RETS (manufactured by Otsuka Densi KK) or amolecular orientation system MOA (manufactured by Oji ScientificInstruments).

The stretched PET film used in the present application may be impartedwith antiglare properties (haze). The method of imparting antiglareproperties is not particularly limited, and for example, a method ofmixing inorganic particulates or organic particulates into the raw resinto form a film, a method of forming a stretched film from anun-stretched film having a layer, in which inorganic particulates ororganic particulates are mixed, on one side, based on the method ofproducing the film, or a method of coating a coating liquid formed bymixing inorganic particulates or organic particulates with a curablebinder resin on one side of a stretched PET film and curing the binderresin to form an antiglare layer, and the like is adopted.

The inorganic particulates for imparting antiglare properties are notparticularly limited, but may include, for example, silica, colloidalsilica, alumina, alumina sol, an aluminosilicate, an alumina-silicacomposite oxide, kaolin, talc, mica, calcium carbonate, and the like.Also, the organic particulates are not particularly limited, but mayinclude, for example, crosslinked polyacrylic acid particles, methylmethacrylate/styrene copolymer resin particles, crosslinked polystyreneparticles, crosslinked polymethyl methacrylate particles, silicone resinparticles and polyimide particles, and the like. The antiglareproperty-imparted stretched PET film thus obtained may have a haze valuein a range of 6 to 45%.

A functional layer such as a conductive layer, a hard coating layer anda low reflective layer may be further laminated on the antiglareproperty-imparted stretched PET film. Furthermore, as the resincomposition constituting the antiglare layer, a resin composition havingany one of these functions may also be selected.

The haze value can be measured using, for example, a haze-permeabilitymeter HM-150 (manufactured by Murakami Color Research Laboratory, Co.,Ltd.) in accordance with JIS K 7136. In the measurement of the hazevalue, in order to prevent the film from being warped, for example, ameasurement sample in which the film surface is bonded to a glasssubstrate using an optically transparent pressure-sensitive adhesive sothat the antiglare property-imparted surface becomes the surface can beused.

The functional layer other than the antiglare layer or the like can belaminated on one side or both sides of the stretched PET film used inthe present application, unless it interferes with the effect of thepresent application. The functional layer to be laminated may include,for example, a conductive layer, a hard coating layer, a smoothinglayer, an easily slipping layer, an anti-blocking layer and an easyadhesion layer, and the like.

The above-described method for producing a PET film is one exemplarymethod for obtaining the polymer film substrate of the presentapplication, where as long as the polymer film substrate applicable inthe present application has the above-described physical properties, anykind of commercially available product can also be used.

In one example, the polymer film substrate may be a film substrate thatan electrode layer is formed on one side. Such a film substrate may bereferred to as an electrode film substrate. The above-mentionedretardation or mechanical properties, and the like may be for thepolymer film substrate on which the electrode layer is not formed, orfor the electrode film substrate.

In the case of the electrode film substrate, each of electrode layersmay be formed on at least one side of the polymer film substrate, andfirst and second polymer film substrates may be disposed so that theelectrode layers face each other.

As the electrode layer, a known transparent electrode layer may beapplied, and for example, a so-called conductive polymer layer, aconductive metal layer, a conductive nanowire layer, or a metal oxidelayer such as ITO (indium tin oxide) may be used as the electrode layer.Besides, various materials and forming methods capable of forming atransparent electrode layer are known, which can be applied withoutlimitation.

In addition, an alignment film may be formed on one side of the polymerfilm substrate, for example, the upper part of the electrode layer inthe case of the electrode film substrate. A known liquid crystalalignment film can be formed as the alignment film, and the kind ofalignment film that can be applied according to a desired mode is known.

As described above, in the present application, the light modulationlayer included in the light modulation film layer is a functional layercapable of changing the transmittance, reflectivity and/or haze of lightdepending on whether or not an external signal is applied. Such a lightmodulation layer in which the state of light changes depending onwhether or not an external signal is applied, or the like, can bereferred to as an active light modulation layer herein. In one example,when the light modulation layer is a layer containing a liquid crystalcompound, the light modulation layer may be referred to as an activeliquid crystal layer, where the active liquid crystal layer means aliquid crystal layer in a form that the liquid crystal compound can bechanged in the active liquid crystal layer by application of theexternal signal. Also, the light modulation film layer comprising theactive liquid crystal layer may be referred to as an active liquidcrystal film layer.

The external signal herein may mean any external factors, such as anexternal voltage, that may affect the behavior of a material containedin the light modulation layer, for example, a light modulating material.Therefore, the state without external signal may mean a state where noexternal voltage or the like is applied.

In the present application, the type of the light modulation layer isnot particularly limited as long as it has the above-describedfunctions, and a known light modulation layer can be applied. In oneexample, the light modulation layer may be a liquid crystal layer, and astructure including a liquid crystal layer between the first and secondpolymer film substrates arranged opposite to each other may also bereferred to as a liquid crystal cell or an active liquid crystal filmlayer herein.

An exemplary light modulation device can have excellent durabilityagainst gas permeability. In one example, the light modulation devicemay have a void generation rate of 20% or less upon being stored at atemperature of 60° C. and 85% relative humidity. The void generationrate may mean a percentage of the number of void generation samplesrelative to the number of samples used in the void generationevaluation. In another example, the first and second polymer filmsubstrates may be substrates heat-treated at a temperature of 130° C.for 1 hour, where the light modulation device comprising such polymerfilm substrates may not cause voids due to the inflow of external gasfor 500 hours when stored at a temperature of 60° C. and 85% relativehumidity. This can be achieved by disposing the transverse directions ofthe first and second polymer film substrates so as to be parallel toeach other, as described above.

In one example, the light modulation layer may be an active liquidcrystal layer comprising liquid crystal molecules (liquid crystal host)and dichroic dyes. Such a liquid crystal layer may be referred to as aguest host liquid crystal layer (GHLC layer). In this case, thestructure comprising the light modulation layer between the polymer filmsubstrates may be referred to as an active liquid crystal film layer. Inthis specification, the term “GHLC layer” may mean a layer that dichroicdyes may be arranged together depending on arrangement of liquid crystalmolecules to exhibit anisotropic light absorption characteristics withrespect to an alignment direction of the dichroic dyes and the directionperpendicular to the alignment direction, respectively. For example, thedichroic dye is a substance whose absorption rate of light varies with apolarization direction, where if the absorption rate of light polarizedin the long axis direction is large, it may be referred to as a p-typedye, and if the absorption rate of polarized light in the short axisdirection is large, it may be referred to as an n-type dye. In oneexample, when a p-type dye is used, the polarized light vibrating in thelong axis direction of the dye may be absorbed and the polarized lightvibrating in the short axis direction of the dye may be less absorbed tobe transmitted. Hereinafter, unless otherwise specified, the dichroicdye is assumed to be a p-type dye, but the type of the dichroic dyeapplied in the present application is not limited thereto.

In one example, the GHLC layer may function as an active polarizer. Inthis specification, the term “active polarizer” may mean a functionalelement capable of controlling anisotropic light absorption depending onapplication of external action. For example, the active GHLG layer cancontrol the anisotropic light absorption for the polarized light in thedirection parallel to the arrangement direction of dichroic dyes and thepolarized light in the vertical direction by controlling the arrangementof liquid crystal molecules and dichroic dyes. Since the arrangement ofliquid crystal molecules and dichroic dyes can be controlled by theapplication of external action such as a magnetic field or an electricfield, the active GHLC layer can control anisotropic light absorptiondepending on the application of external action.

The kind and physical properties of the liquid crystal molecules can beappropriately selected in consideration of the object of the presentapplication.

In one example, the liquid crystal molecules may be nematic liquidcrystals or smectic liquid crystals. The nematic liquid crystals maymean liquid crystals in which rod-like liquid crystal molecules have noregularity about positions but are arranged in parallel to the long axisdirection of the liquid crystal molecules, and the smectic liquidcrystals may mean liquid crystals in which rod-like liquid crystalmolecules are regularly arranged to form a layered structure and arealigned in parallel with the regularity in the long axis direction.According to one example of the present application, nematic liquidcrystals may be used as the liquid crystal molecules.

In one example, the liquid crystal molecules may be non-reactive liquidcrystal molecules. The non-reactive liquid crystal molecules may meanliquid crystal molecules having no polymerizable group. Here, thepolymerizable group may be exemplified by an acryloyl group, anacryloyloxy group, a methacryloyl group, a methacryloyloxy group, acarboxyl group, a hydroxyl group, a vinyl group or an epoxy group, andthe like, but is not limited thereto, and a known functional group knownas the polymerizable group may be included.

The refractive index anisotropy of the liquid crystal molecules can beappropriately selected in consideration of target physical properties,for example, variable transmittance characteristics. In thisspecification, the term “refractive index anisotropy” may mean adifference between an extraordinary refractive index and an ordinaryrefractive index of liquid crystal molecules. The refractive indexanisotropy of the liquid crystal molecules may be, for example, 0.01 to0.3. The refractive index anisotropy may be 0.01 or more, 0.05 or more,0.07 or more, 0.09 or more, or 0.1 or more, and may be 0.3 or less, 0.2or less, 0.15 or less, 0.14 or less, or 0.13 or less.

When the refractive index anisotropy of the liquid crystal molecules iswithin the above range, it is possible to provide a light modulationdevice having excellent variable transmittance or reflectancecharacteristics. In one example, the lower the refractive index of theliquid crystal molecules is in the above range, the light modulationdevice having more excellent variable transmittance or reflectancecharacteristics can be provided.

The dielectric constant anisotropy of the liquid crystal molecules mayhave positive dielectric constant anisotropy or negative dielectricconstant anisotropy in consideration of a driving method of a targetliquid crystal cell. In this specification, the term “dielectricconstant anisotropy” may mean a difference between an extraordinarydielectric constant (ce) and an ordinary dielectric constant (co) of theliquid crystal molecules. The dielectric constant anisotropy of theliquid crystal molecules may be, for example, in a range within ±40,within ±30, within ±10, within ±7, within ±5 or within ±3. When thedielectric constant anisotropy of the liquid crystal molecules iscontrolled within the above range, it may be advantageous in terms ofdriving efficiency of the light modulation element.

The liquid crystal layer may comprise a dichroic dye. The dye may beincluded as a guest material. The dichroic dye may serve, for example,to control the transmittance of the light modulation device depending onorientation of a host material. In this specification, the term “dye”may mean a material capable of intensively absorbing and/or deforminglight in at least a part or all of the ranges within a visible lightregion, for example, within a wavelength range of 400 nm to 700 nm, andthe term “dichroic dye” may mean a material capable of anisotropicabsorption of light in at least a part or all of the ranges of thevisible light region.

As the dichroic dye, for example, a known dye known to have propertiesthat can be aligned depending on the alignment state of the liquidcrystal molecules by a so-called host guest effect can be selected andused. An example of such a dichroic dye includes a so-called azo dye, ananthraquinone dye, a methine dye, an azomethine dye, a merocyanine dye,a naphthoquinone dye, a tetrazine dye, a phenylene dye, a quaterrylenedye, a benzothiadiazole dye, a diketopyrrolopyrrole dye, a squalene dyeor a pyromethene dye, and the like, but the dye applicable in thepresent application is not limited thereto. As the dichroic dye, forexample, a black dye can be used. Such a dye is known, for example, asan azo dye or an anthraquinone dye, and the like, but is not limitedthereto.

As the dichroic dye, a dye having a dichroic ratio, that is, a valueobtained by dividing the absorption of the polarized light parallel tothe long axis direction of the dichroic dye by the absorption of thepolarized light parallel to the direction perpendicular to the long axisdirection, of 5 or more, 6 or more, or 7 or more, can be used. The dyemay satisfy the dichroic ratio in at least a part of the wavelengths orany one wavelength within the wavelength range of the visible lightregion, for example, within the wavelength range of about 380 nm to 700nm or about 400 nm to 700 nm. The upper limit of the dichroic ratio maybe, for example, 20 or less, 18 or less, 16 or less, or 14 or less orso.

The content of the dichroic dye in the liquid crystal layer can beappropriately selected in consideration of the object of the presentapplication. For example, the content of the dichroic dye in the liquidcrystal layer may be 0.1 wt % or more, 0.25 wt % or more, 0.5 wt % ormore, 0.75 wt % or more, 1 wt % or more, 1.25 wt % or more, or 1.5 wt %or more. The upper limit of the content of the dichroic dye in theliquid crystal layer may be, for example, 5.0 wt % or less, 4.0 wt % orless, 3.0 wt % or less, 2.75 wt % or less, 2.5 wt % or less, 2.25 wt %or less, 2.0 wt % or less, 1.75 wt % or less, or 1.5 wt % or less. Whenthe content of the dichroic dye in the liquid crystal layer satisfiesthe above range, it is possible to provide a light modulation devicehaving excellent variable transmittance characteristics. In one example,the higher the content of the dichroic dye is in the above range, thelight modulation device having more excellent variable transmittancecharacteristic can be provided.

In the liquid crystal layer, the total weight of the liquid crystalmolecules and the dichroic dye may be, for example, about 60 wt % ormore, 65 wt % or more, 70 wt % or more, 75 wt % or more, 80 wt % ormore, 85 wt % or more, 90 wt % or more, or 95 wt % or more, and inanother example, it may be less than about 100 wt %, 98 wt % or less, or96 wt % or less.

The liquid crystal layer can switch the orientation state depending onwhether or not a voltage is applied. The voltage may be applied to adirection vertical or horizontal to the polymer film substrate.

In one example, the liquid crystal layer of the active liquid crystalfilm layer can be designed to switch from any one state selected to ahorizontal orientation state, a vertical orientation state and a twistedorientation state to another state.

In one example, the liquid crystal layer may be present in a horizontalorientation state or a twisted orientation state when no voltage isapplied, and may be present in a vertical orientation state when avoltage is applied. In the twisted orientation state, the twisted anglemay be, for example, more than about 0 degrees and 360 degrees or less.The liquid crystal cell in a horizontal orientation state may bereferred to as an ECB (electrically controllable birefringence) modeliquid crystal cell, and the liquid crystal cell in a twistedorientation state may be referred to as a TN (twisted nematic) mode orSTN (super twisted nematic) mode liquid crystal cell. The TN mode liquidcrystal cell may have a twist angle of more than 0 degrees to 90 degreesor less, and according to one embodiment of the present application, thetwist angle in the TN mode may be about 10 degrees or more, about 20degrees or more, about 30 degrees or more, about 40 degrees or more,about 50 degrees or more, about 60 degrees or more, about 70 degrees ormore, about 80 degrees or more, or about 90 degrees or so.

In the STN mode, the twist angle may be about 100 degrees or more, about110 degrees or more, about 120 degrees or more, about 130 degrees ormore, about 140 degrees or more, about 150 degrees or more, about 160degrees or more, about 170 degrees or more, about 180 degrees or more,about 190 degrees or more, about 200 degrees or more, about 210 degreesor more, about 220 degrees or more, about 230 degrees or more, about 240degrees or more, about 250 degrees or more, about 260 degrees or more,about 270 degrees or more, about 280 degrees or more, about 290 degreesor more, about 300 degrees or more, about 310 degrees or more, about 320degrees or more, about 330 degrees or more, about 340 degrees or more,or about 350 degrees or more, or may be about 270 degrees, or about 360degrees or so.

The liquid crystal molecules in the horizontally oriented liquid crystallayer may be present in a state where a light axis is horizontallyaligned with the plane of the liquid crystal layer. For example, thelight axes of the liquid crystal molecules may form an angle in a rangeof about 0 to 20 degrees, 0 to 15 degrees, 0 to 10 degrees, or 0 to 5degrees, or of about 0 degrees with respect to the plane of the liquidcrystal layer. The light axes of the liquid crystal molecules in thehorizontally aligned liquid crystal layer may be parallel to each otherand may form, for example, an angle in the range of 0 to 10 degrees, 0to 5 degrees, or of about 0 degrees.

In the liquid crystal layer of the twisted orientation, the liquidcrystal molecules may have a spiral structure in which the light axesare oriented in layers while being twisted along a virtual helix axis.The light axis of the liquid crystal molecule may mean the slow axis ofthe liquid crystal molecule, where the slow axis of the liquid crystalmolecule may be parallel to the long axis of the rod-shaped liquidcrystal molecule. The helix axis may be formed to be parallel to thethickness direction of the liquid crystal layer. In this specification,the thickness direction of the liquid crystal layer may mean a directionparallel to a virtual line connecting the lowermost portion and theuppermost portion of the liquid crystal layer at the shortest distance.In one example, the thickness direction of the liquid crystal layer maybe a direction parallel to a virtual line formed in a directionperpendicular to the surface of the polymer substrate. In thisspecification, the twisted angle means an angle formed by the light axisof the liquid crystal molecule existing at the lowermost portion of thetwisted orientation liquid crystal layer and the light axis of theliquid crystal molecule existing at the uppermost portion.

The liquid crystal molecules in the vertically oriented liquid crystallayer may be present in a state where the light axes are arrangedperpendicular to the plane of the liquid crystal layer. For example, thelight axes of the liquid crystal molecules may form an angle of about 70to 90 degrees, 75 to 90 degrees, 80 to 90 degrees or 85 to 90 degrees,preferably 90 degrees with respect to the plane of the liquid crystallayer. The light axes of the plurality of liquid crystal molecules inthe vertically oriented liquid crystal layer may be parallel to eachother and may form an angle in the range of, for example, 0 to 10degrees or 0 to 5 degrees, or of about 0 degrees.

The ratio (d/p) of the thickness (d) and the pitch (p) of the liquidcrystal layer in the twisted orientation liquid crystal layer may be 1or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 orless, 0.4 or less, 0.3 or less, or 0.2 or less. If the ratio (d/p) isout of the range, for example, more than 1, finger domains may occur.The ratio (d/p) may be, for example, more than 0, 0.1 or more, 0.2 ormore, 0.3 or more, 0.4 or more, or 0.5 or more. Here, the thickness (d)of the liquid crystal layer may be synonymous with the cell gap of theliquid crystal cell.

The pitch (p) of the twisted orientation liquid crystal layer may bemeasured by a measuring method using a wedge cell, and specifically, itmay be measured by a method described in Simple method for accuratemeasurement of the cholesteric pitch using a “stripe-wedgeGrandjean-Cano cell of D. Podolskyy, et al. (Liquid Crystals, Vol. 35,No. 7, July 2008, 789-791).

The liquid crystal layer may further comprise a chiral dopant fortwisted orientation. The chiral agent that can be included in the liquidcrystal layer can be used without particular limitation as long as itcan induce a desired rotation without deteriorating the liquidcrystallinity, for example, the nematic regularity. The chiral agent forinducing rotation in the liquid crystal molecules needs to include atleast chirality in the molecular structure. The chiral agent may beexemplified by, for example, a compound having one or two or moreasymmetric carbons, a compound having an asymmetric point on aheteroatom, such as a chiral amine or a chiral sulfoxide, or a compoundhaving axially asymmetric and optically active sites such as cumulene orbinaphthol. The chiral agent may be, for example, a low molecular weightcompound having a molecular weight of 1,500 or less. As the chiralagent, commercially available chiral nematic liquid crystals, forexample, chiral dopant liquid crystal S-811 available from Merck Co.,Ltd. or LC756 available from BASF may also be used.

The application ratio of the chiral dopant is selected so as to achievethe above ratio (d/p), which is not particularly limited. In general,the content (wt %) of the chiral dopant is calculated by an equation of100/HTP (helical twisting power)×pitch (nm), and an appropriate ratiocan be selected in consideration of the desired pitch with reference tothis method.

The thickness of the liquid crystal layer may be appropriately selectedin consideration of the object of the present application. The thicknessof the liquid crystal layer may be, for example, about 0.01 μm or more,0.1 μm or more, 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more,5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, or10 μm or more. The upper limit of the thickness of the liquid crystallayer may be, for example, about 30 μm or less, 25 μm or less, 20 μm orless, or 15 μm or less. When the thickness of the liquid crystal layersatisfies the above range, it is possible to provide a light modulationdevice having excellent variable reflectance characteristics. In oneexample, the thinner the thickness of the liquid crystal layer is in theabove range, the light modulation device having more excellent variablereflectance characteristics can be provided.

The light modulation device may further comprise first and secondalignment films present inside the first and second polymer filmsubstrates, respectively, as the above-described alignment film. In thisspecification, the inside of the first and second polymer filmsubstrates may mean a side where the light modulation layer is present,and the outside may mean the opposite side to the side where the lightmodulation layer is present.

As the first and second alignment films, a horizontal alignment film ora vertical alignment film may be applied. In one example, the first andsecond alignment films may all be horizontal alignment films. In anotherexample, any one of the first and second alignment films may be ahorizontal alignment film and the other may be a vertical alignmentfilm. According to the light modulation element of the presentapplication, when a horizontal alignment film and a vertical alignmentfilm are applied to the first and second alignment films, respectively,the driving voltage characteristic can be improved as compared with acase where a horizontal alignment film is applied to each of the firstand second alignment films.

The light modulation device can adjust the transmittance, reflectanceand haze by adjusting the orientation state of the liquid crystal layeraccording to whether or not a voltage is applied. The orientation stateof the liquid crystal layer can be controlled by a pretilt of thealignment film.

In this specification, the pretilt may have an angle and a direction.The pretilt angle may be referred to as a polar angle, and the pre-tiltdirection may also be referred to as an azimuthal angle.

The pretilt angle may mean an angle in which the light axis of theliquid crystal molecule forms with respect to a horizontal plane of thealignment film. In one example, the vertical alignment film may have apretilt angle of about 70 degrees to 90 degrees, 75 degrees to 90degrees, 80 degrees to 90 degrees, or 85 degrees to 90 degrees. In oneexample, the pretilt angle of the horizontal alignment film may be about0 to 20 degrees, 0 to 15 degrees, 0 to 10 degrees, or 0 to 5 degrees.

The pretilt direction may mean a direction in which the light axis ofthe liquid crystal molecule is projected on a horizontal plane of thealignment film. The pretilt direction may be an angle formed by theprojected direction and the horizontal axis (WA) of the liquid crystallayer. In this specification, the horizontal axis (WA) of the liquidcrystal layer may mean a direction parallel to the long axis directionof the liquid crystal layer, or a direction parallel to the lineconnecting both eyes of an observer wearing eyewear or an observerobserving a display device when a light modulation element is applied tothe eyewear or the display device such as a TV.

The pretilt directions of the first alignment film and the secondalignment film can be appropriately adjusted in consideration of theorientation of the liquid crystal layer. In one example, the pretiltdirections of the first alignment film and the second alignment film maybe parallel to each other for horizontal orientation, the pretiltdirections of the first alignment film and the second alignment film mayform 90 degrees to each other for twisted orientation having a twistedangle of 90 degrees and the pretilt directions of the first alignmentfilm and the second alignment film may be parallel to each other fortwisted orientation having a twisted angle of 360 degrees. When thepretilt directions of the first alignment film and the second alignmentfilm are parallel to each other, the pretilt directions of the firstalignment film and the second alignment film may be anti-parallel toeach other, and for example, may form 170 degrees to 190 degrees, 175degrees to 185 degrees, preferably 180 degrees to each other.

The alignment film can be selected and used without particularlimitation as long as it has orientation ability with respect toadjacent liquid crystal layers. As the alignment film, for example, acontact type alignment film such as a rubbing alignment film or a photoalignment film known to be capable of exhibiting orientation propertiesby a non-contact method such as irradiation of linearly polarized lightby including a photo alignment film compound can be used.

It is known to adjust the pretilt direction and angle of the rubbingalignment film or the photo alignment film. In the case of the rubbingalignment film, the pretilt direction can be parallel to the rubbingdirection, and the pretilt angle can be achieved by controlling therubbing conditions, for example, the pressure condition upon rubbing,the rubbing intensity, and the like. In the case of the photo alignmentfilm, the pretilt direction can be controlled by the direction ofpolarized light to be irradiated and the like, and the pretilt angle canbe controlled by the angle of light irradiation, the intensity of lightirradiation, and the like.

In one example, each of the first and second alignment films may be arubbing alignment film. When the rubbing directions of the first andsecond alignment films are disposed to be parallel to each other, therubbing directions of the first and second alignment films may beanti-parallel to each other, and for example, may form 170 degrees to190 degrees, 175 degrees to 185 degrees, preferably 180 degrees to eachother. The rubbing direction can be confirmed by measuring the pretiltangle, and since the liquid crystals generally lie along the rubbingdirection and simultaneously generate the pretilt angle, it is possibleto measure the rubbing direction by measuring the pretilt angle. In oneexample, the transverse directions of the first and second polymer filmsubstrates may each be parallel to the rubbing axis of any one of thefirst and second alignment films.

The light modulation device may further comprise, as the electrodelayers, first and second electrode layers present inside the first andsecond polymer film substrates, respectively. When the light modulationdevice comprises the first and second alignment films, the firstelectrode layer may exist between the first polymer film substrate andthe first alignment film, and the second electrode layer may existbetween the second polymer film substrate and the second alignment film.

The light modulation element may further comprise an antireflectivelayer. In one example, the light modulation element may further comprisefirst and/or second antireflective layers present outside the firstand/or second polymer film substrates, respectively. As theantireflective layer, a known antireflective layer may be used inconsideration of the object of the present application, and for example,an acrylate layer may be used. The antireflective layer may have athickness of, for example, 200 nm or less, or 100 nm or less.

The light modulation element may further comprise an ultravioletabsorbing layer. In one example, the light modulation element mayfurther comprise first and second ultraviolet absorbing layers presentoutside the first and second polymer film substrates, respectively. Asthe ultraviolet absorbing layer, a known ultraviolet absorbing layer maybe suitably selected and used in consideration of the object of thepresent application.

In one example, the light modulation device can be formed by directlycoating the antireflective layer, the ultraviolet absorbing layer, andthe like on the polymer film substrate. If the first and second polymerfilm substrates are used, it may be advantageous in terms of refractiveindex matching and coating process optimization. In this case, there areadvantages that the process can be simplified and the thickness of theelement can be reduced. In another example, in the light modulationdevice, the antireflective layer or the ultraviolet absorbing layer maybe formed on one side of a base film, and the base film may be attachedto the polymer film substrate via a pressure-sensitive adhesive or anadhesive.

The light modulation device of the present application may furthercomprise a reflective layer together with the light modulation filmlayer (active liquid crystal film layer).

In a first embodiment, the reflective layer may be a mirror reflectivelayer. In this case, the light modulation device may further comprise aquarter wavelength plate between the active liquid crystal film layerand the reflective layer.

The quarter wavelength plate may be directly coated on one side of thepolymer film substrate of the active liquid crystal film layer, or maybe attached via a pressure-sensitive adhesive or an adhesive. Thequarter wavelength plate may mean a retardation layer having quarterwavelength phase retardation characteristics. In this specification, theterm “n-wavelength phase retardation characteristic” may mean acharacteristic that the incident light can be phase-delayed by n timesthe wavelength of the incident light within at least a part of thewavelength range. The quarter wavelength plate may have in-planeretardation for a wavelength of 550 nm, for example, in a range of 110nm to 220 nm or 130 nm to 170 nm.

The quarter wavelength plate may be a liquid crystal film or a polymerstretched film.

The liquid crystal film may comprise a polymerizable liquid crystalcompound in a polymerized state. In the present application, the“polymerizable liquid crystal compound” may mean a compound containing amoiety capable of exhibiting liquid crystallinity, such as a mesogenskeleton, and containing one or more polymerizable functional groups.The phrase “a polymerizable liquid crystal compound is contained in apolymerized form” may mean a state where the liquid crystal compound ispolymerized to form a skeleton such as a main chain or a side chain ofthe liquid crystal polymer in the liquid crystal polymer film. Thepolymerizable liquid crystal compound may be contained in the liquidcrystal film, for example, in a horizontally oriented state.

The polymer stretched film may be, for example, a film in which alight-transmitting polymer film capable of imparting optical anisotropyby stretching is stretched in a suitable manner. The polymer film may beexemplified by, for example, a polyolefin film such as a polyethylenefilm or a polypropylene film, a cycloolefin polymer (COP) film such as apolynorbornene film, a polyvinyl chloride film, a polyacrylonitrilefilm, a polysulfone film, a polyacrylate film, a polyvinyl alcohol filmor a cellulose ester-based polymer film such as a TAC (triacetylcellulose) film, or a copolymer film of two or more monomers among themonomers forming the polymer, and the like. In one example, as thepolymer film, a cycloolefin polymer film can be used. Here, thecycloolefin polymer may be exemplified by a ring-opening polymer of acycloolefin such as norbornene or a hydrogenated product thereof, anaddition polymer of a cycloolefin, a copolymer of another comonomer,such as an alpha-olefin, with a cycloolefin, or a graft polymer that thepolymer or copolymer is modified with an unsaturated carboxylic acid ora derivative thereof, and the like, but is not limited thereto.

In one example, the slow axis of the quarter wavelength plate and theaverage light axis of the liquid crystal molecules of the active liquidcrystal layer upon applying no voltage may be within the range of 40 to50 degrees or 43 to 47 degrees, or about 45 degrees, to each other. Inthis specification, the average light axis may mean the vector sum ofthe light axes of the liquid crystal molecules of the liquid crystallayer.

When the angle formed by the slow axis of the quarter wavelength plateand the average light axis of the liquid crystal molecules of the liquidcrystal layer is within the above range, it is possible to exhibitexcellent antireflection characteristics in the blocking state, and thusit may be advantageous to improve the variable reflectancecharacteristics.

In the light modulation device, the reflective layer may be present onone side of the quarter wavelength plate. Also, the reflective layer maybe directly coated on one side of the quarter wavelength plate, or maybe attached via a pressure-sensitive adhesive or an adhesive.

The reflective layer may have a mirror reflection characteristic. Themirror reflection characteristic may be referred to as regularreflection or specular reflection. In one example, the reflective layermay have a reflectance of 20% to 100% for light with a wavelength of 400to 700 nm.

The reflective layer may be, for example, a metal thin film layercomprising a metal having high reflectance for the entire visible light,such as silver, gold, magnesium, nickel, bismuth, chromium, copper,calcium, strontium, aluminum or an alloy thereof.

The light modulation device of the first embodiment can exhibit variablereflectance characteristics according to the orientation state of theliquid crystal layer depending on whether or not a voltage is applied.That is, the light modulation device of the first embodiment can switchbetween low reflection mode and high reflection mode states as describedabove.

The light modulation device may be in a blocking state indicating aminimum reflectance upon applying no voltage to the liquid crystallayer, and may be in a reflective state indicating a maximum reflectanceupon voltage application.

In one example, the light modulation device may have a differencebetween reflectance upon applying a voltage of 15V and reflectance uponno voltage application of 20% to 60%.

In a second embodiment of the present application, the reflective layermay be a reflective polarizer. In this case, as the reflective layer,two reflective polarizers may be included. For example, the secondembodiment may sequentially comprise the above-mentioned active liquidcrystal film layer, and the first reflective polarizer, the additionallight modulation film layer and the second reflective polarizer.

The light modulation film layer may be configured similarly to theactive liquid crystal film layer, and for example, may comprise thethird and fourth polymer film substrates disposed opposite to eachother, and the active liquid crystal layer present between the third andfourth polymer film substrates and comprising a liquid crystal compound.The second and fourth substrates may be asymmetric film substrates ofthe same kind as the above-mentioned active liquid crystal film layersubstrate, or may be other kinds of substrates.

The active liquid crystal layer (hereinafter, may be referred to as thesecond liquid crystal layer) of the light modulation film layer maycomprise no dichroic dye. The contents described in the item of liquidcrystal molecules of the active liquid crystal film layer may be equallyapplied to the liquid crystal compound of the second liquid crystallayer. Hereinafter, for convenience, the liquid crystal layer comprisingthe liquid crystal molecules (liquid crystal host) and the dichroic dyeof the above-mentioned active liquid crystal film layer may be referredto as a first liquid crystal layer.

The first and second liquid crystal layers can change their orientationstates depending on whether or not a voltage is applied. The voltage maybe applied in a direction perpendicular to the polymer film substrate.

In the second embodiment, the first liquid crystal layer can be designedso as to switch between the vertical orientation state and thehorizontal orientation state. For example, it may exist in a verticallyoriented state upon no voltage application and may exist in ahorizontally oriented state upon voltage application. Such a liquidcrystal layer may be referred to as a VA (vertical alignment) modeliquid crystal layer.

The second liquid crystal layer can switch between the horizontalorientation state and the twisted orientation state. For example, it mayexist in a twisted orientation state upon no voltage application and mayexist in a horizontally oriented state upon voltage application. Such aliquid crystal cell may be referred to as a TN (twisted nematic) modeliquid crystal cell. The twisted angle in the twisted orientation statemay be more than 0 degrees to 90 degrees or less, and according to oneembodiment of the present application, the twisted angle in the TN modemay be about 10 degrees or more, about 20 degrees or more, about 30degrees or more, about 40 degrees or more, about 50 degrees or more,about 60 degrees or more, about 70 degrees or more, about 80 degrees ormore, or about 90 degrees or so.

The above-described contents can be equally applied to the state of thelight axes of the liquid crystal molecules in the vertically orientedliquid crystal layer and the light axes of the liquid crystal moleculesin the horizontally oriented liquid crystal layer.

Also, the above-described contents can be equally applied to the mattersabout the state of the light axes of the liquid crystal molecules in thetwisted orientation liquid crystal layer, the twisted angle, the ratio(d/p) between the thickness (d) and the pitch (p) and the measurementmethod thereof.

The liquid crystal layer may further comprise a chiral dopant fortwisted orientation, where the matters about the specific types andratios of the chiral dopant used are also the same as theabove-described contents.

The thicknesses of the first and/or second liquid crystal layers can beappropriately selected in consideration of the object of the presentapplication. The thickness of the liquid crystal layer may be, forexample, about 0.01 μm or more, 0.1 μm or more, 1 μm or more, 2 μm ormore, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm ormore, 8 μm or more, 9 μm or more, or 10 μm or more. The upper limit ofthe thickness of the liquid crystal layer may be, for example, about 30μm or less, 25 μm or less, 20 μm or less, or 15 μm or less. When thethickness of the liquid crystal layer satisfies the above range, it ispossible to provide a light modulation device having excellent variablereflectance characteristics. In one example, the thinner the thicknessof the liquid crystal layer is in the above range, a light modulationdevice having more excellent variable reflectance characteristics can beprovided.

The light modulation device may comprise an alignment film existing onthe polymer film substrate of the active liquid crystal film layer andan alignment film existing on the substrate of the light modulation filmlayer. Hereinafter, for convenience of explanation, the four alignmentfilms are referred to as first to fourth alignment films, respectively,where the first and second alignment films are the alignment filmsinside the substrate of the active liquid crystal film layer,respectively, and the third and fourth alignment films are the alignmentfilms inside the substrate of the light modulation film layer,respectively. In this specification, the inside of the substrate is thesurface of the substrate facing the light modulation layer or the activeliquid crystal layer.

A horizontal alignment film or a vertical alignment film may be appliedto each of the first to fourth alignment films. In one example, each ofthe first and second alignment films may be a vertical alignment film.In one example, each of the third and fourth alignment films may be ahorizontal alignment film, or any one of the third and fourth alignmentfilms may be a horizontal alignment film and the other may be a verticalalignment film. According to the light modulation device of the presentapplication, the case of applying a horizontal alignment film and avertical alignment film to the third and fourth alignment films,respectively can improve the driving voltage characteristics as comparedwith the case of applying horizontal alignment films to the third andfourth alignment films, respectively.

The light modulation device can adjust the transmittance, reflectanceand haze by adjusting the orientation state of the liquid crystal layerdepending on whether or not a voltage is applied. The orientation stateof the liquid crystal layer can be controlled by the pretilt of thealignment film, where the contents of the pretilt are similar to theabove-described contents.

The pretilt directions of the first alignment film and the secondalignment film can be appropriately adjusted in consideration of theorientation of the first liquid crystal layer. Also, the pretiltdirections of the third alignment film and the fourth alignment film canbe appropriately adjusted in consideration of the orientation of thesecond liquid crystal layer. In one example, the pretilt directions ofthe first alignment film and the second alignment film may be parallelto each other for the vertical orientation upon no voltage application,and the pretilt directions of the first alignment film and the secondalignment film may form 90 degrees to each other for the twistedorientation having a twisted angle of 90 degrees. When the pretiltdirections of the first alignment film and the second alignment film areparallel to each other, the pretilt directions of the first alignmentfilm and the second alignment film may be anti-parallel to each other,which may be, for example, in a range of 170 degrees to 190 degrees or175 degrees to 185 degrees, or approximately 180 degrees, to each other.In one example, the transverse directions of the first and secondpolymer film substrates may be each parallel to the rubbing axis of anyone of the first and second alignment films. In one example, thetransverse directions of the third and fourth polymer film substratesmay be each parallel to the rubbing axis of any one of the third andfourth alignment films.

The alignment film can be selected and used without particularlimitation as long as it has orientation ability with respect toadjacent liquid crystal layers, and specific types are also similar tothe above-described contents.

In one example, each of the first to fourth alignment films may be arubbing alignment film. When the rubbing directions of the first andsecond alignment films are disposed to be parallel to each other, therubbing directions of the first and second alignment films may beanti-parallel to each other, which may be, for example, in a range of170 degrees to 190 degrees or 175 degrees to 185 degrees, orapproximately 180 degrees, to each other. The rubbing direction can beconfirmed by measuring the pretilt angle, and since the liquid crystalsgenerally lie along the rubbing direction and simultaneously generatethe pretilt angle, it is possible to measure the rubbing direction bymeasuring the pretilt angle.

The light modulation device may further comprise first and secondelectrode layers present inside the first and second polymer filmsubstrates, respectively, and may further comprise third and fourthelectrode layers present inside the third and fourth polymer filmsubstrates, respectively. When the light modulation device comprisesfirst, second, third and fourth alignment films, the first electrodelayer may exist between the first polymer film substrate and the firstalignment film, the second electrode layer may exist between the secondpolymer film substrate and the second alignment film, the thirdelectrode layer may exist between the third polymer film substrate andthe third alignment film, and the fourth electrode layer may existbetween the fourth polymer film substrate and the second alignment film.

Similarly to the first embodiment, the light modulation element of thesecond embodiment may further comprise an antireflective layer and anultraviolet absorbing layer, and the like.

The light modulation device may comprise the first reflective polarizerof the active liquid crystal film layer including the first liquidcrystal layer. The first reflective polarizer may be directly coated onone side of the polymer film substrate of the active liquid crystal filmlayer, or may be attached via a pressure-sensitive adhesive or anadhesive

The reflective polarizer may have selective transmission and reflectioncharacteristics. For example, the reflective polarizer may have aproperty of transmitting one component of transverse wave andlongitudinal wave components of light and reflecting the othercomponent. When light is incident on the reflective polarizer, lighttransmitted through the reflective polarizer and light reflected fromthe reflective polarizer may have polarization characteristics. In oneexample, the polarization direction of the transmitted light and thepolarization direction of the reflected light may be orthogonal to eachother. That is, the reflective polarizer may have a transmission axisand a reflection axis orthogonal to the plane direction.

As the reflective polarizer, for example, a reflective polarizer knownas a so-called DBEF (dual brightness enhancement film) or a reflectivepolarizer formed by coating a liquid crystal compound such as LLC(lyotropic liquid crystal) may be used.

Since the reflective polarizer has a characteristic of transmitting mostof one component of transverse wave and longitudinal wave components oflight and reflecting most of the other component, it can be realized inthe form of a half mirror. In one example, the reflective polarizer mayhave a reflectance of about 50% or more for unpolarized incident light.According to one example of the present application, for example, a DBEF(dual brightness enhancement film) may be used as the reflectivepolarizer.

In one example, the reflection axis of the first reflective polarizerand the average light axis of the liquid crystal molecules of the liquidcrystal layer upon horizontal orientation of the first liquid crystallayer may form 0 to 10 degrees, 0 to 5 degrees or approximately 0degrees. The average light axis may mean the vector sum of the lightaxes of the liquid crystal molecules in the liquid crystal layer.

When the angle formed by the reflection axis of the first reflectivepolarizer and the average light axis of the liquid crystal molecules inthe first liquid crystal layer is within the above range, it is possibleto exhibit excellent antireflection characteristics in the blockingstate, and thus it may be advantageous to improve the variablereflectance characteristics.

The light modulation device may comprise the light modulation film layeron one side of the first reflective polarizer. The first reflectivepolarizer may be directly coated on one side of the substrate of thelight modulation film layer, or may be attached via a pressure-sensitiveadhesive or an adhesive.

In one example, the reflection axis of the first reflective polarizerand the light axis of the liquid crystal molecule closest to the firstreflective polarizer in the liquid crystal layer upon the twistedorientation of the second liquid crystal layer of the light modulationfilm layer may form an angle in the range of 80 degrees to 110 degreesor 85 degrees to 105 degrees, or of about 90 degrees.

Also, in one example, the reflection axis of the first reflectivepolarizer and the light axis of the liquid crystal molecule farthestfrom the first reflective polarizer in the liquid crystal layer upon thetwisted orientation of the second liquid crystal layer of the lightmodulation film layer may form an angle in the range of 0 to 10 degreesor 0 to 5 degrees, or an angle of about 0 degrees.

When the angles formed by the reflection axis of the first reflectivepolarizer and the light axes of the liquid crystal molecules of thesecond liquid crystal layer are within the above range, it is possibleto exhibit excellent antireflection characteristics in the blockingstate, and thus it may be advantageous to improve the variablereflectance characteristics.

The light modulation device may further comprise the second reflectivepolarizer on one side of the light modulation film layer having thesecond liquid crystal layer. The second reflective polarizer may bedirectly coated on the substrate of the light modulation film layerhaving the second liquid crystal layer, or may be attached via apressure-sensitive adhesive or an adhesive. Unless otherwise specifiedwith respect to the second reflective polarizer, the contents describedabout the first reflective polarizer can be equally applied.

The reflection axis of the second reflective polarizer and thereflection axis of the first reflective polarizer may form an angle inthe range of 0 to 10 degrees or 0 to 5 degrees, or about 0 degrees. Whenthe angle formed by the reflection axis of the second reflectivepolarizer and the reflection axis of the first reflective polarizer iswithin the above range, it is possible to exhibit excellentantireflection characteristics in the blocking state, and thus it may beadvantageous to improve the variable reflectance characteristics.

The light modulation device may exhibit variable reflectancecharacteristics according to the orientation state of the liquid crystallayer depending on whether or not a voltage is applied. That is, thelight modulation device can switch between the high reflection mode andthe low reflection mode as described above.

The light modulation device may be in a reflective state that exhibits amaximum reflectance when a voltage is not applied to the liquid crystallayer and may be in a blocking state that exhibits a minimum reflectancewhen a voltage is applied. The light modulation device has excellentvariable reflectance characteristics depending on whether or not avoltage is applied. In one example, the light modulation device may havea difference between the reflectance upon applying a voltage of 10V andthe reflectance upon no voltage application of 30% to 50%. Thereflectance may be a value measured at a tilt angle of 20 degrees.

The light modulation device can be applied to various applications inwhich variable reflectance characteristics are required. Theapplications in which variable reflectance characteristics are requiredcan be exemplified by openings in enclosed spaces including buildings,containers or vehicles, and the like, such as variable materials forvehicles, variable reflectance mirrors, room mirrors, windows orsunroofs, or eyewear, and the like. Here, in the range of eyewear, alleyewear formed so that an observer can observe the outside throughlenses, such as general glasses, sunglasses, sports goggles or helmets,or instruments for experiencing augmented reality, can be included.

A typical application to which the light modulation device can beapplied is eyewear. When the light modulation device is applied toeyewear, the structure of the eyewear is not particularly limited. Thatis, the light modulation element may be mounted and applied in a lensfor a left eye and/or a right eye having a known eyewear structure.

For example, the eyewear may comprise a left eye lens and a right eyelens; and a frame for supporting the left eye lens and the right eyelens.

FIG. 2 is an exemplary schematic diagram of the eyewear, which is aschematic diagram of the eyewear comprising a frame (82), and left eyeand right eye lenses (84), but the structure of the eyewear to which thelight modulation device can be applied is not limited to FIG. 2. In theeyewear, the left eye lens and the right eye lens may each comprise thelight modulation device. Such a lens may comprise only the lightmodulation device, or may also comprise other configurations.

Advantageous Effects

The present application can provide a light modulation device bothexcellent mechanical properties and optical properties by applying anoptically and mechanically anisotropic polymer film as a substrate.

Mode for Invention

Hereinafter, the present application will be specifically described byway of Examples, but the scope of the present application is not limitedby the following examples.

The polymer film substrates used in Examples or Comparative Examples area PC (polycarbonate) film substrate (PC substrate, thickness: 100 μm,manufacturer: Teijin, product name: PFC100-D150), which is an isotropicfilm substrate usually applied as a substrate, and a PET (polyethyleneterephthalate) film substrate (SRF substrate, thickness: 80 μm,manufacturer: Toyobo, product name: TA044), which is an asymmetricsubstrate according to the present application, and the followingphysical properties are the results of measurement in a state where anITO (indium tin oxide) film having a thickness of about 20 nm is formedon one side of each film substrate.

1. Phase Retardation Evaluation of Polymer Film Substrate

The in-plane retardation value (Rin) of the polymer film substrate wasmeasured for light having a wavelength of 550 nm using a UV/VISspectroscope 8453 instrument from Agilent Co., Ltd. according to thefollowing method. Two sheets of polarizers were installed in the UV/VISspectroscope so that their transmission axes were orthogonal to eachother, and a polymer film was installed between the two sheets ofpolarizers so that its slow axis formed 45 degrees with the transmissionaxes of the two polarizers, respectively, and then the transmittanceaccording to wavelengths was measured. The phase retardation order ofeach peak is obtained from the transmittance graph according towavelengths. Specifically, a waveform in the transmittance graphaccording to wavelengths satisfies Equation A below, and the maximumpeak (Tmax) condition in the sine waveform satisfies Equation B below.In the case of λmax in Equation A, since the T of Equation A and the Tof Equation B are the same, the equations are expanded. As the equationsare also expanded for n+1, n+2 and n+3, arranged for n and n+1 equationsto eliminate R, and arranged for n into λn and λn+1 equations, thefollowing Equation C is derived. Since n and λ can be known based on thefact that T of Equation A and T of Equation B are the same, R for eachof λn, λn+1, λn+2 and λn+3 is obtained. A linear trend line of R valuesaccording to wavelengths for 4 points is obtained and the R value forthe equation 550 nm is calculated. The function of the linear trend lineis Y=ax+b, where a and b are constants. The Y value when 550 nm has beensubstituted for x of the function is the Rin value for light having awavelength of 550 nm.

T=sin²[(2πR/λ)]  [Equation A]

T=sin²[((2n+1)π/2)]  [Equation B]

n=(λn−3λn+1)/(2λn+1+1−2λn)   [Equation C]

In the above, R denotes in-plane retardation (Rin), λ denotes awavelength, and n denotes a nodal degree of a sine waveform.

2. Evaluation of Tensile Property and Coefficient of Thermal Expansionof Polymer Film Substrate

A tensile strength test was conducted according to the standard byapplying a force at a tensile speed of 10 mm/min at room temperature(25° C.) using UTM (Universal Testing Machine) equipment (Instron 3342)to measure the elastic modulus (Young's modulus), elongation and maximumstress of the polymer film substrate. In this case, each specimen wasprepared by tailoring it to have a width of about 10 mm and a length ofabout 30 mm, and both ends in the longitudinal direction were each tapedby 10 mm and fixed to the equipment, and then the evaluation wasperformed.

A length expansion test was conducted according to the standard whileelevating the temperature from 40° C. to 80° C. at a rate of 10° C./minusing TMA (thermomechanical analysis) equipment (Metteler toledo,SDTA840) to measure the coefficient of thermal expansion. Upon themeasurement, the measurement direction length of the specimen was set to10 mm and the load was set to 0.02 N.

The evaluation results of physical properties of each film substratemeasured in the above manner are shown in Table 1 below.

In Table 1 below, MD and TD are MD (machine direction) and TD(transverse direction) directions of the PC substrate and the SRFsubstrate which are stretched films, respectively, and 45 is thedirection forming 45 degrees with both the MD and TD directions.

TABLE 1 Coefficient Elastic Elon- Maximum of Thermal Direc- Rin modulusgation Stress Expansion tion (nm) (GPa) (%) (MPa) (ppm/° C.) PC MD 12.11.6 13.6 63.4 119.19 Sub- TD 1.6 11.6 62.3 127.8 strate SRF MD 14800 2.56.1 81.5 83.3 Sub- 45 15176 3.2 60.4 101.6 52.2 strate TD 15049 5.8 44.7184.6 21.6

EXAMPLE 1

Two SRF substrates were used to manufacture a light modulation device.An alignment film was formed on an ITO (indium tin oxide) film(electrode layer) of the SRF substrate (width: 15 cm, length: 5 cm) toprepare a first substrate. As the alignment film, one obtained byrubbing a polyimide-based horizontal alignment film (SE-7492, Nissan)having a thickness of 300 nm with a rubbing cloth was used. A secondsubstrate was prepared in the same manner as the first substrate. Thefirst and second substrates were disposed opposite to each other so thattheir alignment films faced each other, a GHLC mixture (MDA-16-1235,Merck) comprising a liquid crystal compound having a positive dielectricconstant anisotropy with a refractive index anisotropy (AN) of 0.13 anda dichroic dye was positioned therebetween, and then the frame wassealed to prepare an active liquid crystal film layer. The active liquidcrystal film layer is in an ECB mode, and the cell gap is 6 μm. Here,the TD directions (slow axis directions) of the first and secondsubstrates were each 0 degrees based on the rubbing axis of the firstsubstrate alignment film, and the rubbing directions of the first andsecond alignment films were anti-parallel to each other. Subsequently, ageneral mirror (reflective layer) was disposed on one side of the activeliquid crystal film layer to produce an optical device. The reflectivelayer is a general mirror having an average reflectance of about 95% forlight of 400 nm to 700 nm.

COMPARATIVE EXAMPLE 1

A light modulation device was manufactured in the same manner as inExample 1, except that a PC substrate was applied as a substrate.

TEST EXAMPLE 1

Using the light modulation devices of Example 1 and Comparative Example1, an eyewear element of the type shown in FIGS. 3 and 4 wasmanufactured, and a heat shock test was conducted in a state of bendingthe element. The heat shock test was performed by setting a step ofraising the temperature of the eyewear from about −40° C. to 90° C. at atemperature increase rate of about 16.25° C./min and then maintaining itfor 10 minutes, and again reducing the temperature from 90° C. to −40°C. at a temperature decrease rate of about 16.25° C./min and thenmaintaining it for 10 minutes as one cycle and repeating the cycle 500times, where this test was conducted with the eyewear attached to abending jig having a curvature radius of about 100R. FIG. 3 showed thecase of Example 1 and FIG. 4 showed the case of Comparative Example 1,where in the case of Comparative Example 1, severe cracks were observedas in the drawing.

COMPARATIVE EXAMPLE 2

A light modulation device was manufactured in the same manner as inExample 1, except that the first directions (TD directions) of the firstand second substrates were set to 90 degrees to each other. At thistime, based on the rubbing direction of the alignment film on the firstsubstrate, the first direction of the first substrate was 0 degrees andthe first direction of the second substrate was 90 degrees.

COMPARATIVE EXAMPLE 3

A light modulation device was manufactured in the same manner as inExample 1, except that the first directions (TD directions) of the firstand second substrates were set to 90 degrees to each other. At thistime, based on the rubbing direction of the alignment film on the firstsubstrate, the first direction of the first substrate was 45 degrees andthe first direction of the second substrate was 135 degrees.

TEST EXAMPLE 2

The void generation was evaluated while the devices of Example 1,Comparative Examples 2 and 3 were each stored at 60° C. and 85% relativehumidity, and the results were shown in Table 2 below. Specifically, itwas evaluated whether or not the visually observed voids occurred in thelight modulation layer while being kept under the above conditions.Generally, the size of the visually observed voids is about 10 μm.

TABLE 2 Number of Number Number First samples of bad of good occurrenceinitially void void Void time of introduced samples samples incidencevoid Comparative 2 12 12 0 100% 120 h Example 3 12 12 0 100% 144 hExample 1 12 1 11  8% 504 h

As results of Table 2, in the case of Comparative Examples 2 and 3,voids were observed within 500 hours in all of the initially introducedsamples to show the void incidence of 100%, and the times when the voidswere first observed were also within 120 hours and 144 hours,respectively.

On the other hand, in the case of Example 1, voids were not observedwithin 500 hours, and the time when the voids were first observed wasalso about 504 hours.

EXAMPLES 2 TO 4

A quarter wavelength plate was placed between the active liquid crystalfilm layer and the reflective layer of the optical device of Example 1to prepare a light modulation device (Example 2). The quarter wavelengthplate is a retardation film formed of a TAC (tri-acetyl-cellulose) film.

An electro-optical characteristic and occurrence of a rainbow phenomenonwere evaluated for the light modulation device. The electro-opticalcharacteristic was evaluated for the light modulation device bymeasuring a change in reflectance depending on whether or not a voltagewas applied. Specifically, the reflectance according to the appliedvoltage was measured using a reflection spectroscope (CM-2600d, KonicaMinolta) while an AC power was connected to the electrode layers of theactive liquid crystal film layer and driven. The reflectance is anaverage of reflectance for light having a wavelength of 380 nm to 780nm.

The evaluation of the rainbow phenomenon is a cognitive evaluation, andit has been evaluated that the rainbow phenomenon occurs when two ormore patterns representing different luminance rather than the sameluminance in the sample are generated.

In the following evaluation example, TN_90° is the result of the casewhere the active liquid crystal layer is constituted by a TN mode havinga twisted angle of 90 degrees (Example 3), and STN_360° is the casewhere the active liquid crystal layer is constituted by an STN modehaving a twisted angle of 360 degrees (Example 4).

In the case of Example 2, the active liquid crystal film layer wasprepared in the same manner as in the case of forming the active liquidcrystal film layer in Example 1, except that 0.18 wt % of a chiraldopant (S811, Merck) was added to the GHLC composition and used, and thefilms were laminated so that the rubbing directions of the alignmentfilms of the first and second substrates were 90 degrees to each other.Also, in the case of Example 3, the active liquid crystal film layer wasprepared in the same manner as in the case of forming the active liquidcrystal film layer in Example 1, except that 0.656 wt % of a chiraldopant (S811, Merck) was added to the GHLC composition, where the ratio(dip) of the thickness (cell gap: d) and the pitch (p) of the liquidcrystal layer in the STN mode is about 0.95.

In the following evaluation example, “0V_R” is the reflectance uponapplying no voltage, “15V_R” is the reflectance upon applying a voltageof 15V, and “ΔT” is a value of “15V_R”-“0V_R.”

TABLE 3 Example 2 Cell Gap 6 μm Δn 0.13 Substrate SRF(parallel) ECB 0V_R 6.1% 15 V_R 39.8% ΔR 33.7% TN_90° 0 V_R 6.5% 15 V_R 39.9% ΔR 33.4%STN_360° 0 V_R 6.3% 15 V_R 39.4% ΔR 33.1% Rainbow Phenomenon No

EXAMPLE 5

The SRF substrate was applied to prepare two active liquid crystal filmlayers. The SRF substrate was tailored to have a width of 15 cm and alength of 5 cm, respectively, and an alignment film was formed on oneside of an ITO (indium tin oxide) film (electrode layer) to prepare twosubstrates. As the alignment film, one obtained by rubbing apolyimide-based vertical alignment film (5661LB3, Nissan) having athickness of 300 nm with a rubbing cloth was used. The prepared twosubstrates were disposed opposite to each other so that their alignmentfilms faced each other, a GHLC composition comprising liquid crystalshaving a negative dielectric constant anisotropy with a refractive indexanisotropy (ΔN) of 0.13 and a dichroic dye (MAT-16-568, Merck) waspositioned therebetween, and the frame was sealed with a sealant to forma first active liquid crystal film layer. At this time, the transversedirections (TD directions) of the first and second substrates were each0 degrees based on the rubbing axis of the first polymer film substrate,and the rubbing directions of the alignment films of the first andsecond substrates were anti-parallel to each other. The first activeliquid crystal film layer is a VA mode liquid crystal cell, and the cellgap is 6 μm.

A second active liquid crystal film layer was prepared in the samemanner as the first active liquid crystal film layer, except that apolyimide-based horizontal alignment film (SE-7492, Nissan) was used asalignment films on two substrates and the films were laminated so thatthe rubbing directions each formed 90 degrees to each other, but at thistime, a liquid crystal composition, in which 0.118 wt % of a chiraldopant (S811, Merck) was added to liquid crystals (MDA-16-1235, Merck)having a positive dielectric constant anisotropy with a refractive indexanisotropy (An) of 0.13, was used for forming a liquid crystal layer.The second active liquid crystal film layer is a TN mode liquid crystalcell having a twisted angle of 90 degrees, and the cell gap is 6 μm.

A DBEF (dual brightness enhancement film, 3M) having a reflectance of45% for unpolarized incident light having a wavelength of 380 nm to 780nm was prepared as the first and second reflective polarizers.

The first active liquid crystal film layer, the first reflectivepolarizer, the second active liquid crystal film layer and the secondreflective polarizer were sequentially laminated to produce a lightmodulation device. The reflection axis of the first reflective polarizerwas parallel to the rubbing axis of the alignment film close to thefirst reflective polarizer among two alignment films of the first activeliquid crystal film layer, and was orthogonal to the rubbing axis of thealignment film close to the first reflective polarizer among twoalignment films of the second active liquid crystal film layer, and thereflection axes of the first and second reflective polarizers wereparallel to each other.

An electro-optical characteristic and occurrence of a rainbow phenomenonwere evaluated for the light modulation device. The electro-opticalcharacteristic was evaluated for the light modulation device bymeasuring a change in reflectance depending on whether or not a voltagewas applied. Specifically, the reflectance according to the appliedvoltage was measured using a reflection spectroscope (CM-2600d, KonicaMinolta) in a state where a mirror having a reflectance of 95% or morewas arranged on one side of the light modulation device, while an ACpower was connected to the first and second ITO layers and driven. Thereflectance is an average of reflectance for light having a wavelengthof 380 nm to 780 nm.

The evaluation of the rainbow phenomenon is a cognitive evaluation, andit has been evaluated that the rainbow phenomenon occurs when two ormore patterns representing different luminance rather than the sameluminance in the sample are generated.

In the following evaluation example, “0V_R” is the reflectance uponapplying no voltage, “15V_R” is the reflectance upon applying a voltageof 15V, and “ΔT” is a value of “15V_R”-“0V_R.” In the followingevaluation example, the reflectance is a result of being measured forlight incident on the direction forming 10 degrees or 20 degrees withthe surface normal direction of the light modulation device.

TABLE 4 Example 5 Fist Cell Gap 6 μm Δn 0.13 Substrate SRF(parallel)Reflectance 0 V_R 48.4% [10 degrees] 15 V_R 3.9% ΔR 44.5% Reflectance 0V_R 43.6% [20 degrees] 15 V_R 3.6% ΔR 40.0% Rainbow Phenomenon No

1. A light modulation device comprising: a first polymer film substrate;a second polymer film substrate; an active liquid crystal layer disposedbetween the first and second polymer film substrates, wherein the activeliquid crystal layer contains a liquid crystal host and a dichroic dyeguest; and a reflective layer, wherein the active liquid crystal layeris capable of switching between a first orientation state and a secondorientation state different from the first orientation state uponapplication of a voltage, each of the polymer film substrates has anin-plane retardation of 4,000 nm or more for light having a wavelengthof 550 nm, a ratio (E1/E2) of an elongation (E1) in a first direction toan elongation (E2) in a second direction perpendicular to the firstdirection of 3 or more, and wherein an angle formed by the firstdirection of the first polymer film substrate and the first direction ofthe second polymer film substrate is in a range of 0 degrees to 10degrees.
 2. The light modulation device according to claim 1, whereineach of the first and second polymer film substrates is an electrodefilm substrate having an electrode layer on one side thereof, andwherein the electrode layers of the first and second polymer filmsubstrates face each other.
 3. The light modulation device according toclaim 1, wherein the first and second polymer film substrates arepolyester film substrates.
 4. The light modulation device according toclaim 1, wherein each of the first and second polymer film substrateshas the elongation (E1) in the first direction of 15% or more.
 5. Thelight modulation device according to claim 1, wherein each of the firstand second polymer film substrates has an elongation (E3) in a thirddirection that is larger than the elongation (El) in the firstdirection, wherein a ratio (E3/E2) of the elongation (E3) in the thirddirection to the elongation (E2) in the second direction is 5 or more,and wherein an angle between the third direction and both of the firstand second directions ranges from 40 degrees to 50 degrees.
 6. The lightmodulation device according to claim 1, wherein each of the first andsecond polymer film substrates has a ratio (CTE2/CTE1) of a coefficientof thermal expansion (CTE2) in the second direction to a coefficient ofthermal expansion (CTE1) in the first direction of 1.5 or more.
 7. Thelight modulation device according to claim 6, wherein the coefficient ofthermal expansion (CTE2) in the second direction is in a range of 5 to150 ppm/° C.
 8. The light modulation device according to claim 1,wherein each of the first and second polymer film substrates has a ratio(YM1/YM2) of an elastic modulus (YM1) in the first direction to anelastic modulus (YM2) in the second direction of 1.5 or more.
 9. Thelight modulation device according to claim 8, wherein the elasticmodulus (YM1) in the first direction is in a range of 4 to 10 GPa. 10.The light modulation device according to claim 1, wherein each of thefirst and second polymer film substrates has a ratio (MS1/MS2) of amaximum stress (MS1) in the first direction to a maximum stress (MS2) inthe second direction of 2 or more.
 11. The light modulation deviceaccording to claim 10, wherein the maximum stress (MS1) in the firstdirection is in a range of 150 to 250 MPa.
 12. The light modulationdevice according to claim 1, wherein the reflective layer is a mirrorreflective layer.
 13. The light modulation device according to claim 12,further comprising a quarter wavelength plate disposed between theactive liquid crystal film layer and the reflective layer.
 14. The lightmodulation device according to claim 1, wherein the reflective layerfurther comprising a first reflective polarizer and a second reflectivepolarizer.
 15. The light modulation device according to claim 14,further comprising: a light modulation film layer having an secondactive liquid crystal layer containing a liquid crystal compound,wherein the active liquid crystal film layer, the first reflectivepolarizer, the light modulation film layer and the second reflectivepolarizer are included in this order.
 16. Eyewear comprising: a left eyelens and a right eye lens; and a frame for supporting the left eye lensand the right eye lens, wherein the left eye lens and the right eye lenseach comprise the light modulation device of claim 1.